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Thursday, December 25, 2003 - Page updated at 12:00 AM

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Q&A: Scientists say risk to humans is small

Seattle Times staff reporters

More questions and answers related to mad-cow disease.

Q: Federal and state officials are assuring people that eating beef is absolutely safe. What's the likelihood that consuming muscle tissue such as steak or tongue from an infected cow will lead to developing the human form of mad-cow disease?

A: Scientists agree that the risk to humans is minuscule, mainly because disease-causing prion proteins concentrate in the animal's brain and spinal cord, which is separated from the meat during slaughter. But British investigators studying their country's epidemic of mad-cow disease — formally known as bovine spongiform encephalopathy (BSE) — found that removal of infected cattle brains and spinal cords at slaughter was not fully effective because of contamination of cutting tools or the carcass itself.

In recent years, laboratory studies have shown that the prions in contaminated tonsils, bone marrow and intestinal-tract tissue from BSE-inoculated cattle can infect mice. And a study last year suggests that prions can multiply in infected muscle tissue in mice.

Q: The infected cow from a Mabton farm was called a "downer" cow? What is that?

A: A downer cow is a sick or injured cow that is unable to walk. Those are often older animals, in which the risk of BSE is highest.

Q: Are all downer cows tested for BSE?

A: Only about 10 percent of downer cows in the U.S. are tested, including all with problems of the central nervous system.

Q: Would banning the sale of downer cows for meat eliminate or reduce the risk of BSE getting into the human food supply?

A: It might reduce the risk, said Clive Gay, Washington State University professor of veterinary medicine and head of the department's field disease investigative unit. "I would not personally be averse (to banning meat from downer cows)," he said.

Critics say the USDA should not allow any meat from downer cows into the food chain. Rep. Gary Ackerman, D-N.Y., sponsored an unsuccessful bill in the House this year that would have banned the processing of any downer animals. A similar bill passed the Senate.

Others point out, however, that some downer cows are not old and simply have injuries, such as a broken leg, that indicate no increased risk of BSE.

Q: How do cattle contract BSE?

A: Most likely through contaminated meat and bone meal fed to the animal as a protein source. Since 1997, the United States and Canada have banned giving feed containing protein from cattle or most other mammals to cows.

The cow may have been imported from another country before the U.S. imposed its current ban on cattle imports from countries where BSE has been identified. Or the U.S. ban on using protein from cattle in feed may have been violated.

Q: How did the Canadian cow discovered with BSE last May contract the disease?

A: That's not certain, but investigators learned that the cow was born in Saskatchewan in 1997, before a similar Canadian ban on feed containing protein was imposed.

Q: Would following organic methods of raising cattle eliminate the risk of BSE?

A: Government rules prohibiting the use of animal protein in cattle feed are the same for all cattle, whether raised organically or not.

Q: Is it legal in the U.S. to sell cattle brains as meat or use them in processed meat products such as sausage, even though brain tissue would be diseased in a cow that had BSE?

A: Brains from untested animals could be sold for meat, but brain is rarely used in U.S. meat products.

Some experts favor banning the sale of cattle brains for meat now that BSE has been found in a U.S. cow.

Q: Would irradiation of beef before sale eliminate BSE?

A: That's very unlikely, says Gay, the WSU professor of veterinary medicine. Though there has been little research involving irradiation and BSE, the disease has proved extremely resistant to destruction by various other means, he said.

Q: Will cooking by any means, including microwaving, or freezing destroy the disease?

A: No.

Q: Can BSE be transmitted to hogs or poultry?

A: There's no evidence that it can, Gay said.

Sheep can contract scrapie, a different form of BSE, but there's no evidence this form can be transmitted from sheep to humans, he said. Some experts have considered the possibility that scrapie in sheep was the original source of BSE in cattle, but that is no longer a prevailing theory, Gay said.

Q: Can a person infected with the human form of mad-cow disease, variant Creutzfeldt-Jakob Disease (vCJD), transmit the disease to someone else through a blood transfusion?

A: The British government last week announced the first case of a person dying of vCJD after receiving a blood transfusion from an infected blood donor. The British health secretary told Parliament that it could not be determined if the patient contracted the disease from the transfusion or from eating contaminated beef.

Q: Are there measures to protect transfusion recipients in the U.S. from the disease?

A: Yes. The Puget Sound Blood Center and other blood centers have followed the FDA guideline in excluding as potential blood donors people who spent six or more cumulative months in the United Kingdom between Jan. 1, 1980, and Dec. 31, 1996.

Q: Can a dog, cat or other family pet contract any form of mad-cow disease (BSE) from pet food?

A: Scientists have not found evidence of BSE in dogs, horses and other family pets such as birds, reptiles and gerbils. But a version of the disease has been found in cats in Europe, mostly in the United Kingdom, according to the U.S. Food and Drug Administration. No such disease has ever been found in a cat in the U.S., the FDA says.

Q: Does family-pet food contain animal parts from cattle or other animals that could be infected?

A: Any animal parts can be used, according to the FDA: However, the agency is considering banning the use of brains or other parts of the nervous system in food for dogs, cats, pigs and poultry. The use of meat and bone meal in cattle feed already is prohibited.

Material from The Associated Press and Reuters is included in this report. Judith Blake: 206-464-2349 or jblake@seattletimes.com.

Copyright © 2003 The Seattle Times Company

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